LED Strip Power Supplies (ART330E)

LED tapes or LEDs strips are increasingly popular in both lighting and decoration. Available with white or even color LEDs and even with circuitry which produces effects, they are an attractive solution and extremely simple to use. However, they require care in the installation and the choice of the right source. See in this article some tips on how to work with these LED strips.

LEDs are increasingly replacing incandescent bulbs (which are a thing of the past) as well as economic and fluorescent lighting as decoration.

With a higher yield, smaller size and much longer durability, they are available in formats which are not possible with ordinary bulbs.

Today, LED strips with self-adhesive features can be achieved in rolls and used at any length.

Figure 1

However, it is not enough to have a tape and simply plug it in a power supply so that the LEDs work properly. You need to know how to do this and mainly make the correct choice of source according to the amount of LEDs that should be fed.

Mouser Electronics (www.mouser.com) distributes the products of one of the largest source manufacturers for LEDs, Meanwell (www.meanwell.com).

Mean Well's power supplies are specifically designed to power LED tapes over a wide range of currents which depend precisely on the type of LED fed, the length of the strip and the type of control that may be desired.

Figure 2- Mean Hell Source available at Mouser Electronics

Working with LEDs on tapes

The LEDs that are purchased in the form of tapes are usually available in 5 meter rollers with a plug that allows their connection to a power source, as shown in Figure 3.

Figure 3 - LED roller with plug for the power source

The recommended power voltage for these LED strips is 12 V, but in normal applications good operation can be obtained in a voltage range of 9 to 12 V, which means that the source does not need to be stabilized in a simpler application.

There are also cases where the tapes are specified to operate with 5 V which facilitates the control through microcontrollable circuits. It should be checked at the time of purchase to feed it with the correct voltage.

The current specified for this roller determines the power supply which can go from 300 mA to more than 3 A, depending on the amount of LEDs.

Normally, when buying a 5-meter roll, one can also acquire the appropriate source for this amount of LEDs, without problems, but there are cases where we will use fewer LEDs.

Figure 4 - complete source for one roller

In this case, we need to know the current of each module to properly size our source that does not need to have the total current of the LEDs of the entire roller.

Looking at a ribbon of LEDs, like the photo, we see that it has cutting marks. These marks determine how we can use smaller tape lengths with fewer LEDs. The tape should be cut at these points if we are going to use fewer LEDs. Cutting to another point, we disable the LEDs of that section.

Figure 5 - Cutting of a ribbon of LEDs with simple feeding

Also note that when making the cut we expose the connection contacts so that they can be connected to a source.

For example, if each sector of our tape requires a current of 50 mA (typical values of the sectors are between 15 and 60 mA, depending on the type), and we will feed 10 sectors (from 50 cm to 1 m, according to the tape ), we know that the source must supply 12V x 500mA.

If we observe the tapes we will see that in each sector we have a number of LEDs which already have a resistor calculated to obtain the desired current.

In a tape where we have white LEDs, for example, the RGB (red, green and blue) LEDs need different currents, so we have 3 resistors of different values ??in a connection like the one shown in Figure 6.

Figure 6 - One segment or block of RGB LEDs

Each block then contains RGB LEDs and 3 resistors so that when the 12V voltage is applied to the current in each one is such that the combination of lights produces white.

In tapes that we can control color, instead of a single power track for the three LEDs we have 3 tracks which can be connected separately to an effect circuit, for example.

Thus, we must separate simple sources with only two output wires, from the sources with the more outputs that can be controlled (DIM), as shown in Figure 7.

Figure 7 - Outputs and inputs of sources according to the control mode

On DIM (Dimmable) models, a PWM control signal from 0 to 10 V or another range causes LED brightness to be controlled. Some allow control through a potentiometer.

If we are going to work with different lengths of segments, we must also have cables with connectors that are adapted to the tapes we cut.

These connectors can be purchased at the same location where you purchased the tapes. The connector should be according to the type of tape, that is, if it has a feed track (single color or white LEDs), or three RGB or colored tracks, and so it can be connected to the control circuit.

For three-color tapes, the connection to its own source can be made as shown in Figure 8.

Figure 8 - Connecting RGB tape

It is clear that a connection through the appropriate connector is much better, as shown in Figure 9.

Figure 9 - Using a connector

Some companies sell the set of LEDs with an automatic circuit of effects. Usually this circuit is sized to control a certain length of LED strips, which should be checked in the user’s manual.

If you want, however, you can create your effects from your Arduino by making the connections as shown in Figure 10 and creating the appropriate program.

See that we cannot use the outputs directly from the Arduino, because the current is insufficient for a good amount of LEDs. We need transistors which can be the BD135 for currents up to 500 mA and the TIP31 for currents up to 2 A, not forgetting the heat sinks and the common ground source, as shown in Figure 10.

Figure 10 - Creating effects with a microcontroller

Mean Well has a large variety of sources which are characterized by the small dimensions that a decoration application requires, since it should normally be built in, due to its resistance to weather, to external applications and yield, since such a source should be economical.

In Figure 11 we have a typical block diagram of a Mean Well switched mode power supply.